1. Field of the Invention
The present invention relates to an enzyme electrode, more specifically to an enzyme electrode using an enzyme/metal particle complex produced by an enzyme reaction, a method of producing the same and use thereof.
2. Description of the Related Art
Enzymes, which are proteins made in living cells and act as biocatalysts, work potently under milder conditions compared to general catalysts. Enzymes have high substrate specificity and generally catalyze only a certain reaction of a certain substrate. Of such enzymes, an enzyme called oxidoreductase catalyzes the redox reaction of a substrate.
If the charge produced in the oxidoreductase by enzyme reaction can be transported to a conductive member, an electrode with low overpotential and high selectivity can be produced utilizing functions of enzymes.
However, the redox center of an oxidoreductase is often positioned deep inside a three-dimensional structure of protein. For this reason, the distance between a redox center and a conductive member is far to effectively transfer electrons to the conductive member, and therefore, direct electron transfer between the active site of an oxidoreductase and a conductive member is generally difficult.
An approach of electrically connecting an enzyme and a conductive member with a substance called a mediator has been widely used (e.g., Adam Heller, J. Phys. Chem. 1992, 96, 3579-3587).
Mediator molecules can diffuse into protein of an enzyme and transfer electrons between it and the redox center of the enzyme only when they come sufficiently close to the redox center of the enzyme. Then, the mediator which has transferred electrons from the active site, i.e., the redox center, of the enzyme, transports the charge to a conductive member by diffusion or electron hopping, whereby the charge in the enzyme reaction is transported to the conductive member.
With recent development in nanotechnology, many methods of preparing metal particles have been reported. Kei Yasui and Nobuo Kimizuka, Chem. Lett. 2005, 34, 416-417 describes an approach of producing gold particles by catalysis of an enzyme, i.e., glucose oxidase. In the document, measurement of infrared spectra and zeta potential indicates that the enzyme is immobilized on the produced gold particles. Further, measurement of circular dichroism spectra suggests denaturation of the enzyme. In addition to this, Maya Zayats, Ronan Barton, Inna Popov and Itamar Willner, Nano Lett. 2004, 5, 21-25 describes an optical glucose sensor utilizing growth of gold particles due to hydrogen peroxide produced by the enzyme reaction of glucose oxidase and increase in plasmon absorption based on the growth.
On the other hand, Alexey A. Vertegel, Richard W. Siegel and Jonathan S. Dordick, Langmuir 2004, 20, 6800-6807 disclose a complex of an enzyme and metal and show that when adsorbed to particles such as gold and silica, activity of functional protein including enzymes is generally significantly reduced.